Central nervous system diseases and disorders affect a wide range of the population with differing severity. Neurological and psychiatric diseases and disorders include major depression, schizophrenia, bipolar disorder, obsessive compulsive disorder (OCD), panic disorder, and posttraumatic stress disorder (PTSD), among others. These diseases and disorders affect a person's thoughts, mood, behavior and social interactions and can significantly impair daily functioning. See, e.g., Diagnostic and Statistical Manual of Mental Disorders, 4th Ed., American Psychiatric Association (2000) (“DSM-IV-TR”); Diagnostic and Statistical Manual of Mental Disorders, 5th Ed., American Psychiatric Association (2013) (“DSM-5”). Furthermore, neuropsychiatric symptoms such as apathy, depression, anxiety, cognitive impairment, psychosis, aggression, agitation, impulse control and sleep disruption are now recognized as core impairments of neurological diseases and disorders such as Alzheimer's and Parkinson's diseases.
While medications exist for some aspects of these diseases, there remains a need for effective treatments for various neurological and psychiatric diseases and disorders. For example, while mood stabilizers such as lithium and valproate, antidepressants and antipsychotic drugs are used to treat mood disorders, more effective medications are necessary. And current antipsychotics may be successful in treating the positive symptoms of schizophrenia but fare less well for the negative and cognitive symptoms. Additionally, current antidepressants are typically effective only for a proportion of subjects suffering from depression. Furthermore, despite the fact that the behavioral and psychiatric symptoms of neurological disease such as Parkinson's disease and Alzheimer's disease are major reasons for the institutionalization of subjects, few drugs exist to treat them.